Operation of pressure stills



Oct. 27, 1931. E. c. HERTHEL OPERATION OF PRESSURE STILLS Original Filed Nov. 21, 1924 Q ATTORNEYS distillate, therefrom. The

Patented Oct. 27, 1931 UNITED STATES PATENT OFFICE.

EUGENE C. HERTHEL, OF CHICAGO, ILLINOIS, ASSIGNOR '10 SINCLAIR BEFININ G COI- PANY, OF NEW YORK, N. Y A CORPORATION OF MINE OPERATION OI PRESSURE STILLS Original application filed November 21, 1924, Serial 170. 751,213. Divided and this application filed February 27, 1928.

This invention relates to improvements in the cracking of heavier hydrocarbon oils, such as gas oil, for the production of lighter hydrocarbon oils, such as gasoline an pressure invention includes improvements in the o eration of pressure cracking stills, particu arly ClIClllatory pressure stills, and improvements n the operation of reflux towers employed in conjunction with pressure cracking stills.

This application is a division of my co Dd. ing application Serial No. 7 51,213, file November 21, 1924.

When heavy hydrocarbons are distilled under pressure, they are cracked with the production of lighter oils. The products of the cracking reaction also include incondensable gases, and carbon or coke, or heavy tar. In the commercial operation of a pressure still, some definite product or group of products, for'exa'mple gasoline or pressure distillate, is usually desired but the va ors escaping from'the still itself may inc udeheavier constituents in addition to the constituents desired in the pressure distillate;

and, in some cases, particularly in the distillation of lighter charging stocks, the escaping vapors may include. vaporized constituents from the charging stock in their original condition. The vapors from the ressure still are commonly subjected to a re uxing operation to effect, to a reateror lessextent, the return of such heavier vaporized constituents to the still for further treatment therein, but, as ordinarily practiced, such methods have nevertheless resulted in the production of distillates containing large amounts of constituents heavier than the desired pressure distillate. For-example, in treatin gas oil for the production of gasoline y such methods, the ressure distillate usually includesa eonsi erable amount of constituents of a kerosene character and others even heavier, so that it has been necessary to subject a relatively large amount of distillate to redistillation to fractionate it into, merchantable products and to se arate the heavier components. Where refining methods involving chemical treatment followed b redistillation have been applied to such dist1llates,th1s has Serial No. 257,353.

resulted in the chemical treatment of an employed for promoting'and controlling in an improved manner a refluxing operation to which the vapors from the pressure still are subjected and for returning tothe pressure still the. heavier constituents of theivapoisv unsuitable as components of the-desired pressure distillate with resulting improvement in the operation of the pressure still itself. Further, reflux from the refluxing operation, in-. cluding such heavier constituents of the vapors, is positively subjected to the cracking temperature before being permitted to again escape from the pressure still as a vapor.

When a charge of oil, such as gas oil, is subected to a cracking temperature in a pressure still, eracking takes place in a gradual and progressive manner. Lighter constituents produced by the cracking operation are vaporized, and other constituents, such as heavier hydrocarbons formed by the cracking operation, may remain and mix with the charge in the still. A small amount of asphaltic or pitch-like constituents is also progressively formed. During the early part of the operation, these itch-like constituents may remain more or ess completely insolution 1n the charge, but with gradual and progressive cracking the amount of such constituents gradually'and progressively increases until the amount of such constituents increases beyond the saturation point when precipitation and deposition of these constituents begins unless size S are taken to prevent it. As the char e becomes supersaturated with the pitchfike constituents, they tend to deposit upon the heating surfaces of the still with consequent danger of overheating and failure of the'heatin'g surfaces if the still is not shut down at more or less frequent intervals for. cleaning. Initially, the entire-charge of oil in the still acts as a solvent for the pitch-like constituents, but, as portions of'the charge are cracked and. vaporized, the solvent efiect of the charge of-E oil decreases while the amount of pitch-iike constituents increases until finally deposition of pitch-iike constituents occurs. 7 p

In a prior application filed July 12, 1922, Serial No. 574,380, there is described an im proved process of cracking hydrocarbon oils according to which the concentration ofpitch-like constituents in the charge is con-v trolled during the operation of the pressure still by" withdrawing pitch-laden tar and introducing fresh charging stock at a regulated rate to maintain the pltch content of the charge below the saturation point. In one aspect, the present invention involves a further improvement upon the process described in this prior application, and similarly may involve carrying out the cracking operation with the introduction of fresh charging stock and the withdrawal of pitchladen tar to maintain the pitch content of the charge below saturation.

According to the present invention, the vapors from the pressure still are subjected to a refluxing operation in direct contact with an oil including constituents corresponding in character to the desired pressure distillate. This oil employed to promote the refluxing operation is more or less completelyvaporized b contact with the vapors from the still and t e cooling effect of the va orization efiects a sharp refluxing of the heavier vapors, particularly of the constituents heavier than the vaporized constituents. In this way, by ulating the amount and character of the uxing oil introduced. into direct contact with the vapors from the still, a sharp frac- -21 se arate tionation between the components suitable in thede'sired pressure distillate and thehe'avier components can be effected, and the character of the pressure distillate as well as of the re fluxed constituents can be more or less closely controlled. The intermediate lighter va ors,

heavier-than the desired pressure distil ate,

which are allowed to escape with thepressure distillate, in ordinary methods of operation, are refluxed and the reflux circulated through heater where itis heated to the crac ing temperature and then returned to the pressure still from which the. vapors escaped. The reflux-from these lighter constituents thereb assists in maintaining the concentration 0 pitch-like constituents producedduring the progress of the cracking operation below the saturation point. The oil employed for rom'otingand' controlling the improved-re uxing operation of the present invention may be a part of the pressure distillate from the same still or from other pressure-stills operated to produce a similar distillate, or other blends or fractions including constituents corresponding in character to constituents ofthe desired distillate may be emplo ed. Where the operation is carried out with the introduction of additional fresh heavier charging stock, the oil em loyed for promoting and controiiing the As compared to ordinary methods ofopera tion, the introduction into direct contact with the vapors in the reflux tower of an oil including a large amount of constituents corresponding to the constituents of the desired pressure distillate and the consequent vaporization of the'introduced oil and refluxing of the heavier; intermediate constituents from the still may'result, where the operation is carried out toproduce a very light fraction, in theconsumption of an excessive amount of heat in revaporizing in a cyclic manner these intermediate constituents with a resulting decrease in therate of cracking. This decrease .in the rate of crackingmay also be accompanied by an inability on the part of the still to; maintain, autogenously, the desired pressure'due to the decreased rate of production ofcracked vapors and fixed gases. In carryingout-the process of the present invention, these conditions-*may. be offset, if encountered, .in any one ofseveral ways. For this' purpose, .the stillpressure may be maintained b -the introduction of an extraneous gas, or t e still pressure maybe reduced'and regulated at a point between the still andthe condenser. Byoperating the pressure still in either. of these ways, the proper still pressure can be maintainedalthough the rate of cracking ma; be; somewhat decreased. An increased sti lpressure, as compared to that employed in ordinary methods, may also be emplolylred to prevent, to a greater or lessextent,t

constituents before theyare further cracked. The operationof the reflux, tower may also be regulated sothat the-pressure distillate escaping includes a somewhat increased amount of the li hter of these intermediate constituents whic tend to be recycled to an excessive extent between the reflux tower and the s't-ill.

Where a circulatory pressure still is employed, in which the oil is-circulated from and to 'abulk supply tank through a heater e revaporization of these intermediate in which it is heated to the cracking temperature, the reflux from the refluxing operation may be introduced to the still in a manner such that it is directed 'through the heater with the'circulating oil so that it also exerts a solvent action in the heater.

The refluxing operation of the present invention may, with particular advantage, be carried out in a heat insulated'reflux tower so that heat exchange is confined to the constituents in direct contact'in the tower, thereby promoting heat'economy, by preventing loss of heat to the air or other external cooling medium, permitting closer regulation and control of the refluxing operation, and effecting a maximum fractionation of the vapors from the still.

While the refluxing operation of the present invention may be carried out in reflux towers of various types, it is carried out with particular advantage in a reflux tower of baflleconstruction having a relatively large area for free passage of the vapors therethrough. A tower of this type ofl'ers important advantages in safety and in ease of control, isreadily repaired,- and has other advantages which will further appear.

The invention will be further described and illustrated in connection with the accompanying drawing which shows, ina somewhat diagrammatic and conventional manner, a pressure still adapted for the practice of the process of the invention; but, it is intended and will be understood that the invention'is not limited "to the specific method of operation so described.

The accompanying drawing represents, in elevation and partly in section, a pressure still adapted for the practice of the process of the invention. The drawing is not intended to be to scale, for example, the storage tanks illustrated may be materiall larger in' actualpractice than is. shown by t e proportions of the drawing. 1

While the process of the invention may be carried out inpressure cracking stills of different types, it is of special value and application in connection with circulatory pressure stills of the character illustrated. This pressure cracking still is of the general construction and operation described and illustrated in United-States Letters Patent No. 1,285,200 granted to the Sinclair Refining Company November 19,1918, on the application of Edward W. Isom.

The pressure still illustrated is made up of the bulk supply tank '5 located away from the heating furnace, the vertically arranged heating tubes 6 located in the heating flue of the furnace, and circulating pipes 7 8 and 9 connecting successively thebulk supply a tank, acirculating'pump 10, the lower end of the heating tubes, and the upper'end of the heating tubes and the bulk supply tank.

-"IV-"A circulating pump may, with advantage,

be employed for circulating the oil from the bulk supply tank through the heating tubes and back to the bulk supply tank; or the circulating pump may be omitted and thermosyphonic action relied upon for maintaining circulation but with decreased still capacity. Arranged above the bulk supply tank is a reflux tower 11 havin a series of bafiles therein and connected wit the vapor dome of the bulk supply tank through the vapor line 12. The vapors from the top of the reflux tower escape through a vapor line 13 to a condenser 14 arranged to discharge into the receiver 15. From the receiver, the condensed distillate'is discharged through valved connec- 8( tion 16 and the uncondensed vapors and gases through the valved connection 17 A connection 18 is provided at the lower part of the circulating connections of the still for pumpiill g out and charging the still, and a tar draw- 0 connection for use during the operation of the still is provided at 19. A connection 20 is also arranged for introducing fresh charging stock into the circulating oil through the bearings of the circulating pump. Where no circulating pump is employed this connection may be arranged to discharge directly into the circulating connections of the still, advantageously in the connection for circulating oilb from the bulk supply tank to the heating tu es.

The pressure may be regulated and reduced by means of a regulating valve 50 interposed between the reflux tower and the condenser, or the still pressure may be maintained through the condenser and the pressure regulated and controlled by a suitable valve or valves arranged beyond the condenser.

ere an extraneous gas is employed for maintaining the still pressure, the gas pressure maybe applied through connection 17 and the still, condenser and receiver maintained in open communication.

A pump 21 is arranged to force oil through connection 32 to a spray-head 33 in the upper end of the reflux tower, and through it into direct contact with the vapors in the reflux tower. This pump is arranged to draw distillate from either the distillate tank 24, connected to the receiver through connection 16, or from any. suitable source delivered through connection 34. The reflux tower is advantageouslyv provided with a heat insulating jacket (not shown) of suitable material, such as asbestos or mineral wool; and the other exposed parts of the pressure still may also with advantage 'be covered with heat insulating material to prevent unnecessary heat loss and to-promote heat economy. A pum 28 is arranged to force additional fresh heavy 12 charging stock from the supply tank 35 into the pressure still through connection 20 and the bearings of the circulating pump 10, into the reflux tower at an intermediate point through the spray-head 36 and connection 37, or into the upper end of the reflux tower through connections 38 and 32. The heavier charging stock maybe introduced into the still through one or more of these channels at the same time and valves 37 and 38 are provided in therespective connections to control and regulate the distribution of the additional heavy charging stock.

An auxiliary heating coil 39 is shown as arranged in the heating flue of the furnace between the firebox and the vertical heating 7 tubes sothat the auxiliary coil is subjected althou h there is not an opencommunication i to the hottest heating gases and the main heating tubes to the tempered heating gases which have passed over the auxiliary coil. This auxiliary coil is arranged so that the refluxfrom the reflux tower, either with or without the admixture ofv fresh charging stock, is circulated therethrough, thus subjecting the reflux to the hottest heating gases and at the same time protectin the heating surfaces over which the pitc containing charge of oil in the still proper is circulated.

For this purpose an auxiliary tankor reservoir 40 is arranged to receive the reflux from the reflux tower through connection 41. This reservoir has a vent pipe 42 leading back to the reflux tower. A valved connection 43 is also provided for discharging reflux from the reflux tower directly into the bulk supply tank 5. The reservoir 40 is-also connected through the pipes 44 and 45 to the feedline of the auxiliar coil. A pump 46 is arranged to pump the oi from the reservoir 40 through the auxiliary coil, while-the connecting pipe 47 permits circulation by gravity and by convection when the pump 46 is not used. The pipe 48 leads from. connection 44 to the bottom of thebulk supply tank for supplying additional oil i'n-case the amount'of reflux is insuflicient to maintain full the auxiliary coil. A connection-49 is also provided for circulating fresh charging stock through the auxiliary coil if desired. A connection 51 is arranged between the inlet 45 of the auxiliary coil and the discharge side of the circulating pump 10, and may be used in starting a still in operation as well as draining the auxiliary .coil and connection pipe when the still is pumped out. The au'xiliaryfcoil .39isar ranged to discharge through connection 52 into the return circulating connection 9 to the bulk supply tank. v V I The auxilia reservoir or tank 40 is shown as located wit in the bulk supply tank 5,

therewlthexcept through the .pipe connections. This location of the auxiliary reservoir is not essential but is convenient and" enables a tank construction tobe used'which does not need-to withstand high pressure as the pressure inside and out is approximately the same. 4

In carrying out the cracking process of the present invention-in the apparatus illustrat- The reflux from the re with any unvaporized constituents of oilin- .ed in the drawing, is-charged with fresh charging stock in the, usual way, for example through connection 18, and brought to the cracking temperature and pressure in the usual manner. The charging stock, for example, may be gas oil or other suitable charging stock which is to be cracked for the trodu'ced directly thereto'in'liquid form), is circulated through the auxiliary heating coil 39 before it is returned to the main body of oil in the still and before it escapes from the pressure still as a; va or. The reflux is thus subjectedto the mac 'ng temperature, and, moreover, a in the apparatus 1llustrated, is subjected to the hottest heating gases. During the preliminary heating operation, or at anytime thereafter if the supply of reflux is for any reason insuflicient to maintain full :the auxiliary coil, oil other than reflux condensate maybe sup lied thereto eitherfrom the bulk'supply tan through connection 48,

from the circulating connection 51, or from an external supply throughconnection 49.

As soon as the pressure from the still has been brought up to the desired point and vapors are being taken off through the reflux tower, or shortly thereafter, the introduction through connection 32 of a fraction correspondingin character to the desired pressure disti late into the top of the tower in direct contact with the vapors therein is begun.- Forexample, in the roduction of gasoline, a gasoline character raction or an oil including gasoline constituents may be introduced into thetop of the reflux tower in this manner. During the initial period of operation, a fraction rom a separate source,

for example distillate .from a precedingrun,

supplied through connection 34, may beemplolyed for introduction into the reflux tower; an during the latter period of operation, the fraction introduced into the reflux tower may be drawn from this same source or a part of the distillate pr'oduc'ed by the stiiQ during the same operation'may be so employed, or a mixture or blend of such distillates or fractions may be used.' As the distillation proceeds, the still charge is maintained by the introduction of additional charging stock, for example gas oil, and-before the pitch content of the charge reaches the saturation point, the withdrawal of tar through connection 19 is begun and the rate of tar draw-off and of fresh charging stock feed is regulated to maintain the pitch content of the charge below the saturation point. The heavier charging stock may be introduced to the still through the bearings of the circulating pump or it may be introduced into the reflux tower at an intermediate point through connection 37 and lighter oil for controlling and regulating the refluxing operation introduced into the upper part of reflux tower so that the final separation between the heavier constituents and the constituents suitable as components of the desired pressure distillate is eflected in the upper part of the tower above the point of introduction of the heavier feed oil.

The lighter oil introduced into the upper portion of the reflux tower when operating as above described is vaporized to a greater or less extent by heat exchange with the va pors from the still and the heavier constituents of the vapors are refluxed by the cooling efl'ected by the vapors. The extent to which this refluxing oil is vaporized depends to a great extent upon the character of the refluxing oil; for example, using a gasoline feed in the production of a asoline distillate the feed ma be complete y vaporized and escape and be condensed with the distillate. Since the constituents of this refluxing feed which are vaporized correspond in character to the desired distillate, heavier components are not introduced into the distillate by .employing such a feed as a refluxing medium.

The apparatus illustrated in the drawing may also be operated in accordance with the process of the invention by introducing all or a part of the heavier charging stock introduced into the reflux tower,into the upper end of the tower in admixture with the lighter oil for controlling and regulating the refluxing operation, in which case the lighter constituents of the mixture will be vaporized in the reflux tower, promoting and controlling the refluxing operation ina manner similar to that which has been described. To the extent that the heavier charging stock is introduced into direct contact with the va ors in the reflux tower, it assists in promoting the refluxing operation and is thereby preheated. Somewhat more effective separation of the heavier constituents may be effected, how ever, by introducing the major part of-the heavier charging stock introduced into the tower at an intermediate point and by introducing lighter oil for controlling and regulating the refluxing operation into the upper part of the tower.

The process of the invention may be carried out in the production of 'a 450 F. end point gasoline with a feed to the reflux tower comprising a major part of gasoline constituents boiling below 450 F. In such an operation the major part of the constituents of the vapors from the still boiling between about 450 F. and 500 F. and substantially all of the heavier vapors-can be refluxed and returned through the auxiliary coil to the still, and, by proper regulation, a gasoline character fraction can be directly produced. The refluxing operation, however, may be regulated so that a pressure distillate including a larger amount of the heavier components is produced. For example, in carrying out the process. of the invention for the production of a distillate containing about 85% of 450 F. end point gasoline, a gas oil character charging stock may be initially charged to the still, the still brought to a cracking pressure of about 125 lbs. per square inch and additional gas oil character stock' supplied to the still and tar withdrawn therefrom during the cracking operation to maintain the still charge approximately constant. .At the same tlme a distillate including about 50% of 450 F. end point gasoline may be introduced into the reflux tower to promote the refluxing operation, as above described.

In carrying out the process of the present invention for the production of a gasoline character distillate from a heavier hydrocarbon oil, a gasoline fraction or distillate which it is desired to blend with the pressure distillate may be employed as the refluxing agent and may be introduced into the reflux tower in direct contact with the hot vapors from the still for this purpose. For example. a straight run gasoline which it is desired to blend with the cracked gasoline may be introduced into the reflux tower in this way. The gasoline fraction introduced into the reflux tower is vaporized by heat exchange with the hot vapors therein and at the same time refluxes to the still the heavier constitu nts of the vapors. The gasoline fraction is thus employed to promote and control the refluxing operation while at the same time it escapes with the pressure distillate and is condensed therewith so that the blending operation is carried out in an improved manner.

Other advantages of the process of the invention are that the distillates roduced thereby are relatively free from tarry constituents of the fresh oil or still charge and the amount of heavier constituents in the pressure distillate which may tend to carry with them objectionable impurities or otherwise interfere with the. refining operations is reduced, further facilitating the refining treatment. The process of the present invention also enables the production of an increased amount of gasoline, or the-desired pressure distillate, due in part to the better fractionation effected in the reflux tower on the pressure still and in art to a reduction in the overcracking of gaso ine constituents condensed during the refluxing operation and subjected to further cracking treatment.

One evidence indicating a decrease in overcrackin of constituents suitable as components o the desired distillate is a decrease in the production of fixed gas. Thus, the amount of fixed gas for one hundred gallons of charge may bereduced to 18 to 20 pounds as compared to 21 to 22 pounds in the ordieconomy may also be eflected in the amount of cooling water, or of other cooling medium, required for cooling and condensing the pressure distillate due .to the concentration of the pressure distillate, and the size of the condenser employed may be correspondingly reduced.

Other advantages of the process of the invention are that 1t assists in making possible i, .a material saving in fuel and'aflords maxi- 0 mum ease and controland simpliclty of op-' oration when applied to the' direct production of a asoline character distillate.

1. An improved method ofcrackmg hydrocarbon oils which comprises heating a body of the oil to a cracklng temperature under pressure in a pressure still by c rculation over externally heated surfaces, subjecting the va rs from the still to a refluxmg operation 1n direct contact wlth a dlstlllate including constituents corresponding in character to the desired distillate, positivelycirculating the reflux from the refluxing operation through a heater and separately eating it to the cracking temperature therein and then introducing it, into the main body of oil being heated in the still. r 2.. An improved method ofcracking hydrocarbon o ls for the production of a gaso line-character distillate, 'which comprises heating a body of the oil to a cracking temgerature under pressure in a pressure still y circulation over externally heated sur faces, subjecting the vapors from the still to a. refluxing operation in direct contact with a distillate includin gasoline-charae ter constituents, ositive y circulating the reflux from the re, uxing operation through a heater and separately heatin it to the cracking temperature therein an then introduc ing it into the main, body'of oil being heated i e still. i

3. An improved method of cracking hydrc a bcn oils, whi h compri es circulating a body of the oil from and to a bulk supply tank through a heater while under pressure, heating the oil to a cracking temperature in the heater, subjecting the vapors formed to a refluxing o ration in direct contact with a distillate inc uding constituents corresponding in character to, the desired distillate, positively circulating the reflux from the re fluxing operation through a separate heater and separately heating it to the cracking temperature therein and then introducing it into the circulating body of oil.

4;. An improved method of cracking hydrocarbon oils which comprises heating a body of the 011 to a cracking temperature under pressure in a pressure still by circulation over externallyheated surfaces, subjecting the vapors from the still to a refluxmg operation, subjecting the vapors from the re uxing operation to a condensing operation to produce a distillate, withdrawing pitch-laden oil from and introducing additional fresh oilinto the bod of oil in the still during the progress 0 the cracking operation, independently introducing a distilla e including a substantial quantity of constituents corresponding in character to constituents of thedistillate/produced from the vapors from the refluxing operation into direct contact with the vapors in-the refluxing operation, ositively circulating the reflux from the re uxing operation throu h' a heater and separately heating it to t e cracking temperature therein and then introducin y it into the main body of oil being heate in-the still.--

5, An improved method of cracking hydrocarbon oils which comprises heating a body of the L011 to a cracking temperature under pressure in a cracking still by circulation over externally heated surfaces, passing the vapors from the still upwardly through a reflux tower, passinguncondensed vapors from the reflux tower to a condenser o produce a distillate, introducing a distillate including constituents corresponding in character to the desired distillate into the upper endof the reflux tower in direct contact with the va Mrs therein, introducing ad ditional fre h or] into the reflux tower at an intermediate point, positively circulating the reflux from the refluxing o eration through a heater and separately heatm itfto the cracking temperature therein .an then introducing it into the main body of oil being heated in the still. a v

In testimony whereof, ,I have subscribed my name, v v.

EUGENE C, HERTHEL, 

